Azimuthal Equidistant

Producer Field Guide

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Producer Field Guide
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The Azimuthal Equidistant projection is mathematically based on a plane tangent to the Earth. The entire Earth can be represented, but generally less than one hemisphere is portrayed, though the other hemisphere can be portrayed, but is much distorted. It has true direction and true distance scaling from the point of tangency.

Construction

Plane

Property

Equidistant

Meridians

Polar aspect: the meridians are straight lines radiating from the point of tangency.

Oblique aspect: the meridians are complex curves concave toward the point of tangency.

Equatorial aspect: the meridians are complex curves concave toward a straight central meridian, except the outer meridian of a hemisphere, which is a circle.

Parallels

Polar aspect: the parallels are concentric circles.

Oblique aspect: the parallels are complex curves.

Equatorial aspect: the parallels are complex curves concave toward the nearest pole; the Equator is straight.

Graticule spacing

Polar aspect: the meridian spacing is equal and increases away from the point of tangency. Parallel spacing is equidistant. Angular and area deformation increase away from the point of tangency.

Linear scale

Polar aspect: linear scale is true from the point of tangency along the meridians only.

Oblique and equatorial aspects: linear scale is true from the point of tangency. In all aspects, the projection shows distances true to scale when measured between the point of tangency and any other point on the map.

Uses

Radio and seismic work, as every place in the world is shown at its true distance and direction from the point of tangency.

USGS uses the oblique aspect in National Atlas and for large-scale mapping of Micronesia.

The polar aspect is used as the emblem of United Nations.

This projection is used mostly for polar projections because latitude rings divide meridians at equal intervals with a polar aspect. Linear scale distortion is moderate and increases toward the periphery. Meridians are equally spaced, and all distances and directions are shown accurately from the central point.

This projection can also be used to center on any point on the Earth (for example, a city) and distance measurements are true from that central point. Distances are not correct or true along parallels, and the projection is neither equal-area nor conformal. Also, straight lines radiating from the center of this projection represent great circles.

Polar Aspect of Azimuthal Equidistant Projection

map_projection_azimuthal_equidistant

This projection is commonly used in atlases for polar maps.